This application relates to evaluation of stress fields and properties in line features formed on substrates.
Measurements of various properties of a substrate and features fabricated on the substrate may have important applications. For example, manufacturing of certain devices requires fabrication of various features and components on a substrate (e.g., a semiconductor or a glass substrate). Such substrate-based integrated devices include, among others, integrated electronic circuits where micro circuit components are formed on a semiconductor substrate, integrated optical devices where micro optical components are fabricated on a substrate, micro-electro-mechanical systems where micro actuators and other mechanical components are fabricated on a semiconductor substrate, flat panel display systems where light-emitting elements, thin-film transistors and other elements are fabricated on a transparent substrate (e.g., a glass), or a combination of two or more of the above devices.
Different materials and different structures are usually formed on the substrate and are in contact with one another. Some devices may also use complex multilayer geometry. Hence, the interfacing of different materials and different structures may cause a complex stress state in each feature due to differences in the material properties and the structure properties at interconnections under different fabrication processes and environmental factors (e.g., variations or fluctuations in temperature). In fabrication of an integrated circuit, for example, the stress state of the interconnect conducting lines may be affected by film deposition, rapid thermal etching, chemical-mechanical polishing, and passivation during the fabrication process.
It is desirable to measure stresses on various features formed on the substrate to improve the design of the device structure, selection of materials, fabrication process, and other aspects of the devices so that the performance and reliability of the device can be enhanced. The stress measurements may be used to assess or evaluate the reliability of materials against failure from such phenomena as electromigration, stress-voiding and hillock formation. The stress measurements may also be used to facilitate quality control of the mechanical integrity and electromechanical functioning of circuit chip dies during large scale production in wafer fabrication facilities. In addition, the stress measurements may be used to improve the design of various thermal treatments (such as temperature excursions during passivation) and chemical and mechanical treatments (such as polishing) to reduce their contribution to the residual stresses in the final device.
A system according to one embodiment of the invention includes an optical detection module to obtain surface curvature information of a substrate-based device which has line features formed on a substrate, and a processing module to produce stress information of the line features based on the curvature information. The optical detection module may include a coherent gradient sensing system to measure the surface gradient of a surface based on phase information in the wavefront of a reflected optical probe beam.
One method according to one embodiment includes first measuring a first curvature of a substrate at a location and along a longitudinal direction of a line feature formed at the location on the substrate and then measuring a second curvature of the substrate at the same location along a transverse direction perpendicular to the longitudinal direction. Next, an analytical function is used to compute stresses on the line feature based on measured first and second curvatures.
Alternatively, stresses of a line feature may be determined before the line feature is formed. In this method, curvatures of a substrate are measured before a film is deposited. Then the film is deposited on the substrate and its curvature is measured. Next, the stress information of the deposited film is obtained and is used to determine stresses on a line feature to be patterned from the film based on an analytical function. This method can be extended to structures where line features are formed over two or more underlying films on the substrate.
Another method determines stress information of line features embedded in trenches of a layer formed on a substrate. The curvatures of the embedded line features are measured by using an optical probe beam to obtain curvature map of the illuminated area based on spatial gradient information in the reflected optical beam. Then measured curvatures are compared to curvatures of the line features computed from an analytical function. The deviation is then used to determine presence of residual stresses.
Yet another method measures curvatures of a line feature and a film from which the line feature is formed as a function of temperature to determine yield temperatures at which the line and the film change their curvature dependence of the temperature from a linear manner to a nonlinear manner. The ratio between a yield stress of the line feature and a yield stress of the film at their respective yield temperatures can then be determined from an analytical function.
These and other features, and associated advantages of will be apparent from the description and drawings, and from the claims.